Method for improving accuracy of block based motion compensation

ABSTRACT

For use in a video image upconversion unit of the type that uses motion compensation to generate an interpolated field using motion vectors, an improved method of motion compensation is disclosed. The method performs motion compensation on a pixel and determines whether a motion vector assigned to the pixel is correct or incorrect. If the motion vector is incorrect, the method sets the value of the pixel to a previously recorded pixel value. The previously recorded pixel value is obtained by calculating for the pixel the difference between the value of a corresponding motion compensated pixel from a previous frame and the value of a corresponding motion compensated pixel from a next field. The difference is then compared with a threshold value. If the difference is less than the threshold value, then the value of the pixel is set equal to the average of the value of the corresponding motion compensated pixel from the previous frame and the value of the corresponding motion compensated pixel from the next field.

TECHNICAL FIELD OF THE INVENTION

The present invention comprises an improved method of block based motioncompensation in a video image upconversion unit of the type that usesblock based motion compensation to generate an interpolated video fieldusing motion vectors. The improved method of the present inventionobtains accurate values for motion compensated pixels when incorrectmotion vectors are assigned to the pixels.

BACKGROUND OF THE INVENTION

A moving video image is transmitted by a video transmitter as a sequenceof frames or pictures. Each frame or picture may be coded individually,but is displayed sequentially at a video rate. Each video frame is madeup of two video fields, an odd video field and an even video field. Morespecifically, an individual frame denoted by the letter “A” is made upof an odd field denoted by the letters “Ao” and an even field denoted bythe letters “Ae.”

When capturing or recording a video sequence, either frames or fieldsmay be captured. When both the odd field and the even field of a videoframe are captured at the same time, the picture is said to be a“progressive” picture. The odd fields and the even fields are notgenerally used to describe progressive pictures. Instead the individualvideo frames (e.g., frame A, frame B) are used to describe progressivepictures. Most movie film material is composed of progressive pictures.

When the odd field and the even field of a video frame are captured atdifferent times, the picture is said to be an “interlaced” picture. Thetwo fields are not combined to be displayed at the same time. Each fieldis treated and displayed separately. Most television material iscomposed of interlaced pictures.

In order to achieve maximum efficiency during the transmission process,not every field or frame is transmitted. That is, some of the individualfields or frames are dropped and are not transmitted. The dropped fieldsor frames are recreated by the video receiver from information takenfrom the fields or frames that are transmitted.

For example, the dropped fields or frames can be recreated simply byrepeating the previous field or frame. Alternatively, if the display isdelayed, the next field or frame that follows the dropped field or framecan be used to take the place of the dropped field or frame. It is alsopossible to replace the dropped field or frame by averaging theneighboring fields or frames on each side of the dropped field or frame.

There are difficulties with these simple approaches. Repeating aprevious field or frame (or using the next following field or frame) inplace of the dropped field or frame causes the perceived image to bejerky even when small motions are depicted in the video image. Averagingthe fields or frames causes the perceived image to be blurred even whenmoderate motions are depicted in the video image.

A well known method for recreating the dropped fields or frames ismotion compensated interpolation. In motion compensated interpolation(also referred to as “bidirectional prediction”) a subsignal with a lowtemporal resolution (typically one half to one third of the frame rate)is coded and the full resolution signal is obtained by interpolation ofthe low resolution signal and the addition of a correction term. Thesignal to be reconstructed by interpolation is obtained by adding acorrection term to a combination of a past and a future reference.

Video sequences exist in various formats. For example, high definition(HD) television video sequences may be displayed in any one of eighteen(18) different formats. The process of converting a video sequence fromone format to another format is called “scan rate conversion.”

Scan rate conversion may be used to reduce image flicker in televisonimages. For example, a European televison video standard specifies afrequency of fifty Hertz (50 Hz). That is, the video fields are to bedisplayed at a rate of fifty fields per second. This televison videorate is not sufficient to prevent noticeable flicker in the televisionimage. To reduce image flicker, the television video rate may beincreased to one hundred Hertz (100 Hz) by interpolating additionalfields between the original fields in the video image.

Scan rate conversion techniques may be used to convert twenty four Hertz(24 Hz) film to sixty Hertz (60 Hz) video images.

Scan rate conversion techniques may also be used to convert thirty Hertz(30 Hz) high definition (HD) camera images to sixty Hertz (60 Hz) videoimages.

The additional fields needed for scan rate conversion may be acquired bysimply repeating the original fields. The preferred method, however, isto use a progressive to interlace conversion using motion compensatedinterpolation.

There is a need in the art for an improved method of motion compensationto generate interpolated fields that will provide a sharp video image.In particular, there is a need in the art for an improved method forobtaining accurate values for motion compensated pixels when incorrectmotion vectors are assigned to the pixels.

SUMMARY OF THE INVENTION

The present invention is designed to be used in a video imageupconversion unit of the type that uses motion compensation to generatean interpolated field using motion vectors. The present inventioncomprises an improved method of motion compensation that performs motioncompensation on a pixel and determines whether a motion vectorassociated with the pixel is correct or incorrect.

If the motion vector is incorrect, the method sets the value of thepixel to a previously recorded pixel value. The previously recordedpixel value is obtained by calculating for the pixel the differencebetween the value of a corresponding motion compensated pixel from aprevious frame and the value of a corresponding motion compensated pixelfrom a next field. The difference is then compared with a thresholdvalue. If the difference is less than the threshold value, then thevalue of the pixel is set equal to the average of the value of thecorresponding motion compensated pixel from the previous frame and thevalue of the corresponding motion compensated pixel from the next field.

The improved method of the invention comprises the steps of (1)calculating for a pixel within an array of n pixels by m pixels thedifference in value between the value of a corresponding motioncompensated pixel from a previous frame and the value of correspondingmotion compensated pixel from a next field, (2) comparing the differencewith a threshold value, (3) setting the value of the pixel with saidarray of n pixels by m pixels equal to the average of the value of thecorresponding motion compensated pixel from said previous frame and thevalue of the corresponding motion compensated pixel of the next field ifthe value of the difference is less than the threshold value, and (4)recording the value for the pixel within the array of n pixels by mpixels.

The improved method of the invention also comprises the steps of (1)calculating for a pixel within a block of pixels the difference in valuebetween the value of a corresponding motion compensated pixel from aprevious frame and the value of a corresponding motion compensated pixelfrom a next field, (2) comparing the difference with a threshold value,and (3) setting the value of the pixel within the block of pixels to theaverage of the value of the corresponding motion compensated pixel fromthe previous frame and the value of the corresponding motion compensatedpixel of the next field, if the value of the difference is less than thethreshold value, and (4) setting the value of the pixel within the blockof pixels equal to the value that was previously recorded for the pixelwhen the pixel was evaluated as a pixel element within the array of npixels by m pixels, if the value of the difference is not less than thethreshold value.

It is a primary object of the present invention to provide an improvedmethod motion compensated upconversion in a video image upconversionunit of the type that uses motion compensation to generate aninterpolated video field using motion vectors.

It is an additional object of the present invention to provide a methodfor obtaining an accurate value for a motion compensated pixel forinclusion in a generated field to be interpolated between a previousframe and a next field.

It is another object of the present invention to provide an improvedmethod for obtaining an accurate value for a motion compensated pixelthat will provide a sharp video image in a generated field to beinterpolated between a previous frame and a next field by determiningwhether the motion vector associated with the pixel is correct orincorrect.

It is also an object of the present invention to provide an improvedmethod for obtaining an accurate value for a motion compensated pixelthat will provide a sharp video image in a generated field to beinterpolated between a previous frame and a next field by providing anaccurate pixel value when the motion vector that is associated with thepixel is incorrect.

It is an additional object of the present invention to provide animproved method for determining a threshold value to be used to obtainan accurate value for a motion compensated pixel that will provide asharp video image in a generated field to be interpolated between aprevious frame and a next field.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention so that those skilled in the art maybetter understand the Detailed Description of the Invention thatfollows. Additional features and advantages of the invention will bedescribed hereinafter that form the subject of the claims of theinvention. Those skilled in the art should appreciate that they mayreadily use the conception and the specific embodiment disclosed as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. Those skilled in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the invention in its broadest form.

Before undertaking the Detailed Description of the Invention, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise” andderivatives thereof, mean inclusion without limitation; the term “or,”is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller,”“processor,” or “apparatus” means any device, system or part thereofthat controls at least one operation, such a device may be implementedin hardware, firmware or software, or some combination of at least twoof the same. It should be noted that the functionality associated withany particular controller may be centralized or distributed, whetherlocally or remotely. Definitions for certain words and phrases areprovided throughout this patent document, those of ordinary skill in theart should understand that in many, if not most instances, suchdefinitions apply to prior, as well as future uses of such defined wordsand phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, wherein likenumbers designate like objects, and in which:

FIG. 1 is a block diagram of an exemplary high definition (HD)progressive to interlace converter that utilizes the improved method ofthe present invention;

FIG. 2 illustrates a series of input progressive frames of a videosignal;

FIG. 3 illustrates a series of output interlace fields of a videosignal;

FIG. 4 illustrates a previous frame A of a video signal showing fivepixels for display at time T;

FIG. 5 illustrates a next field B of a video signal showing acorresponding set of five pixels for display at time T+1;

FIG. 6 illustrates a generated field C of a video signal showing acorresponding set of five pixels generated by motion compensation fordisplay at intermediate time T+½;

FIG. 7 illustrates a group of nine blocks of pixels (containing sixteenpixels in each block) in which a first set of pixels depicts a firstobject moving in a first direction and a second set of pixels depicts asecond object moving in a second direction;

FIG. 8 illustrates a three by three pixel block used to obtain thevalues of a group of nine pixels within the three by three pixel blockfor use in the block based motion compensation method of the presentinvention;

FIG. 9 illustrates the three by three pixel block shown in FIG. 8superimposed on the group of nine blocks of pixels shown in FIG. 7;

FIG. 10 is a flow diagram illustrating a first portion of the improvedmethod of the present invention; and

FIG. 11 is a flow diagram illustrating a second portion of the improvedmethod of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 11, discussed below, and the various embodiments setforth in this patent document to describe the principles of the presentinvention are by way of illustration only and should not be construed inany way to limit the scope of the invention. In the descriptions of theadvantageous embodiments that follow, the improved method of the presentinvention is used in connection with a high definition (HD) progressiveto interlace converter.

The present invention comprises an improved method of block based motioncompensation that selects an appropriate motion compensated pixel byobtaining an accurate value for the motion compensated pixel when anincorrect motion vector has been assigned to the pixel. It is importantto realize that the method of the present invention is not limited touse in an HD progressive to interlace converter. Those skilled in theart will readily understand that the principles of the present inventionmay also be successfully applied in any type of electronic equipmentthat applies motion compensation techniques to video signals. In thedescriptions that follow, the HD progressive to interlace converter isdescribed as an example of an item of equipment in which the improvedmethod of the present invention may be employed.

FIG. 1 illustrates high definition (HD) progressive to interlaceconverter 100. HD progressive to interlace converter 100 receivesstandard definition (SD) video signals from SD input 110 or receives HDvideo signals from HD input 120. As will be explained below in greaterdetail, HD progressive to interlace converter 100 converts progressiveHD material to interlaced format using motion compensation techniques.

HD progressive to interlace converter 100 comprises field and line rateconverter 130. Field and line rate converter 130 comprises an SAA4992integrated circuit (sometimes referred to as FALCONIC for “field andline rate converter integrated circuit”). The SAA4992 integrated circuitis sold commercially by Philips Semiconductors Corporation. Field andline rate converter 130 is capable of performing scan rate conversionsfor SD size video images.

As shown in FIG. 1, field and line rate converter 130 receives SD videosignals from SD input 110 via multiplexer 140. If the input to HDprogressive to interlace converter 100 is an SD input, the SD videoimages simply pass through multiplexer 140 directly to field and linerate converter 130. The SD video images are then output to SD output160.

HD progressive to interlace converter 100 receives HD video signals fromHD input 120. If the input to HD progressive to interlace converter 100is an HD input, the HD video images must be pre-filtered and downsampledto SD size. This is accomplished in pre-filter and downsampler unit 150.The SD video images from pre-filter and downsampler unit 150 are thensent to multiplexer 140 and passed on to field and line rate converter130.

The filter (not shown) in pre-filter and downsampler unit 150 is aconventional low pass filter used to satisfy the Nyquist criteria. Thefilter may comprise an eleven tap filter that uses the following filtertaps: (1) 0.015625 (2) 0 (3) −0.0703125 (4) 0 (5) 0.3046875 (6) 0.5 (7)0.3046875 (8) 0 (9) −0.0703125 (10) 0 and (11)0.015625.

After the HD video images are filtered, they are downsampled by a factorof one or two or three based on the following conditions. The downsamplefactor is set equal to three (1) if the number of pixels per line isgreater than 1440 and less than or equal to 2160, or (2) if the numberof lines per frame is greater than 1152 and less or equal to 1728. Thedownsample factor is set equal to two (1) if the number of pixels perline is greater than 720, or (2) if the number of lines per frame isgreater than 576. If the above described conditions are not met, thenthe video image is an SD video image and no downsampling is required. Inthat case the downsample factor is set equal to one. It is anticipatedthat a video image that is larger than 2160 pixels by 1728 pixels willrequire a downsampling factor of four. At the present time the largestsize video image known to be in use is 1920 pixels by 1080 pixels.

After the downsizing process is completed, an SD size video image isgenerated and sent to field and line rate converter 130 for motionestimation. Field and line rate converter 130 generates motion vectorsfor the downsampled SD size video images. The SAA4992 integrated circuitof field and line rate converter 130 supports a motion vector overlaymode. That is, the motion vectors generated by field and line rateconverter 130 are overlayed on the video images as color data. Thisfeature permits the motion vectors to be read directly from field andline rate converter 130. That is, no additional hardware or softwarefunctionality is needed to obtain the motion vectors.

After the SD motion vectors are obtained, they are sent to motion vectorpost processing unit 170. The SD motion vectors are scaled to HDvelocity (i.e., magnitude) in motion vector post processing unit 170. Aswill be explained more fully, the scaled HD motion vectors are then usedto generate motion compensated interlaced HD fields from HD progressiveframes.

The SAA4992 integrated circuit of field and line rate converter 130functions as a high quality motion estimator. Because the SAA4992integrated circuit of field and line rate converter 130 uses one frameand one field to perform motion estimation, the same technique of usingone frame and one field must be used for motion compensation.

As shown in FIG. 2, the input consists of the progressive frames A, B,C, D, E and F. As previously mentioned, each frame consists of an oddfield and an even field. For example, frame “A” consists of an odd field“Ao” and an even field “Ae.” Similarly, frame “B” consists of an oddfield “Bo” and an even field “Be.” Similar odd and even fields exist forthe other input frames. The term “progressive” as applied to the inputframes (A, B, C, D, E and F) means that the odd field and the even fieldof each frame are taken at the same time and combined together to formtheir respective frame.

As shown in FIG. 3, the output video signals are interlaced in format.The output odd field “Ao” is taken from input frame “A.” The output evenfield “ABe” is obtained by performing motion compensation on frame “A”and on odd field “Bo” of the input sequence. In a similar manner, theoutput odd field “Bo” is taken from input frame “B.” The output evenfield “BCe” is obtained by performing motion compensation on frame “B”and on odd field “Co” of the input sequence. The remaining interlacedoutput video signals shown in FIG. 3 are similarly obtained. In thismanner the temporally missing fields are generated by using (1) theprevious frame, and (2) the next frame, and (3) the motion vectors.

The motion vectors from field and line rate converter 130 are scaled inaccordance with the downsample factor (DSF) that was applied to the HDinput in pre-filter and downsampler unit 150. For example, assume thatmvx(i,j) and mvy(i,j) are the motion vectors in the x and y directions,respectively, that are obtained from field and line rate converter 130.Then the HD motion vectors generated in motion vector post processingunit 170 will be:

mvxHD[(DSF)i, (DSF)j]=(DSF)mvx(i,j)  (1)

mvyHD[(DSF)i, (DSF)j]=(DSF)mvy(i,j)  (2)

It is seen that not only is the velocity (i.e., magnitude) of the motionvectors scaled, but also the position of the motion vectors. This meansthat, if in an SD video image, the motion vector was applicable to ablock of two by two (2×2), in HD it will be applicable to a block of(DSF times 2) by (DSF times 2). In other words, it will be applicable toa block of (2 DSF) by (2 DSF). Therefore, if the downsample factor istwo (DSF=2) then the motion vector for a two by two block (2×2) in SD isapplicable to a four by four block (4×4) in HD. This scaling causes aloss in the accuracy of the motion vector.

The motion vectors that are obtained from field and line rate converter130 are accurate to one fourth (0.25) of a pixel. If the motion vectorsare scaled by a factor of two (2), then it is to be expected that themotion vectors will only be accurate to one half (0.50) of a pixel. Thisis because two times one fourth is equal to one half (2×0.25=0.50).Unfortunately, this expectation is not met because it turns out that themotion vectors are not accurate to one half (0.50) of a pixel. This isdue to the fact that the filtering and downsampling of the HD inputperformed in pre-filter and downsampler unit 150 causes smoothing of thepicture and smoothing of the object motion. The half pixel accuracy cannot be reliably achieved due to the smoothing introduced during thefiltering and downsampling process.

This means that it is not possible to achieve an accuracy of one fourth(0.25) of a pixel by performing simple calculations on the neighboringpixels that surround the pixel in question. It also means that thescaled motion vectors may not be very reliable, especially at the edgesof the video image.

Given a frame, a field, and the associated motion vectors, the task isto upconvert the information into an HD signal while minimizingdistortions and inaccuracies in the video signal. One prior art approachis to average the motion compensated pixels from the frame and thefield. This method works reasonably well if the motion vectors areaccurate. If the motion vectors are not accurate, however, the averagingof the pixels from the frame and the field will produce blurring of thepicture, which can be very noticeable in slow moving areas of the videoimage.

The prior art method of averaging the motion compensated pixels from theframe and the field may be illustrated with an example using the threefigures shown in FIG. 4, FIG. 5 and FIG. 6. FIG. 4 shows a previousframe A of a video signal showing five pixels (A1, A2, A3, A4 and A5)for display at time T. FIG. 5 shows a next field B of a video signalshowing a corresponding set of five pixels (B1, B2, B3, B4 and B5) fordisplay at time T+1. The unit “1” in the expression “T+1” represents oneunit of time between previous frame A and next field B. FIG. 6 shows agenerated field C of a video signal showing a corresponding set of fivepixels (C1, C2, C3, C4 and C5) generated by motion compensation fordisplay at intermediate time T+½ between previous frame A and next fieldB. The unit “½” in the expression “T+½” represents one half unit of timebetween previous frame A and generated field C.

Consider pixel C4 in generated field C. The task is to find and generatethe appropriate value for this pixel. Pixel A4 in previous frame A isthe motion compensated pixel in previous frame A that corresponds topixel C4. Pixel B4 in next field B is the motion compensated pixel innext field B that corresponds to pixel C4. The prior art averagingmethod adds the value of pixel A4 to the value of pixel B4 and dividesthe sum of the values by two to obtain the value of pixel C4.

This prior art method of averaging is sequentially applied to averageeach pixel in previous frame A with its corresponding pixel in nextfield B to create an averaged set of pixels for generated field C.

In contrast, the improved method of the present invention considers eachpixel individually and determines whether the motion vector associatedwith the pixel under consideration is accurate. If the motion vector forthe pixel under consideration is accurate, then the averaging method isused for that pixel. If the motion vector for the pixel underconsideration is not accurate, the averaging method is not used.Instead, as will be more fully explained, a more accurate value for thepixel is used that has been previously recorded during the motioncompensation process.

In the improved method of the present invention, the HD motion vectorsfrom motion vector post processing unit 170 are sent to HD upconversionunit 180. As shown in FIG. 1, HD upconversion unit 180 is also connectedto HD input 120 and receives the input HD video signal from HD input120. HD upconversion unit 180 than has the following data: (1) themotion vectors from the SD video image appropriately scaled, and (2) theHD frame, and (3) the HD field, and (4) the causal region of the motioncompensated field. The causal region is a region of the motioncompensated field that is made up of pixels whose motion compensatedvalues have already been calculated.

As previously indicated, the values of the motion vectors are good inthe global sense but they are not accurate to one half (0.50) of apixel. The motion vectors may only be accurate to one or two pixels.This means that when the prior art averaging method is used, the edgeswill exhibit blurring. In order to avoid blurring the video image, theimproved method of the present invention averages the frame motioncompensated pixel with the field motion compensated pixel only when themotion vector for the pixel is accurate. When the motion vector for thepixel in not accurate, the improved method of the present inventionselects and uses a previously recorded value of the pixel. If a previousvalue of the pixel has not been recorded, the improved method of thepresent invention uses some other motion compensation method to obtain avalue of the pixel.

The improved method of the present invention may be illustrated with anexample using the three figures shown in FIG. 7, FIG. 8 and FIG. 9. FIG.7 illustrates a group of one hundred forty four (144) pixels dividedinto nine (9) blocks, each of which contains sixteen (16) pixels. Thesixteen (16) pixels in each block are arranged in a four by four array.The empty circles represent a first set of pixels that depict a firstobject that is moving from left to right. The filled circles represent asecond set of pixels that depict a second object that is moving from topto bottom.

In the center of each block containing a four by four pixel array is anarrow that represents a motion vector for the block. Blocks 710, 720,730, 740, and 770, each contain a motion vector indicating movement fromleft to right. Blocks 750, 760, 780, and 790, each contain a motionvector indicating movement from top to bottom. Blocks 710, 720, 730,740, and 770 each contain only pixels that are represented by emptycircles. Block 790 contains only pixels that are represented by filledcircles. Blocks 750, 760, and 780, each contain some pixels that arerepresented by empty circles and some pixels that are represented byfilled circles.

In block based motion compensation, it is common for a block to containpixels that represent two different objects in a video image. It is alsocommon for the two different objects to be moving in differentdirections. Ideally, there should be a motion vector assigned to thedirection of motion of each different section in such a block.Unfortunately, that is not the case. The motion vector estimator willselect only one motion vector for each block. The motion vector that isusually selected (by most types of motion vector estimators) is one thatgives the least sum of absolute differences.

The assignment of only one motion vector to each block means that it ispossible that some pixels within a block will have correct motionvectors and some pixels within the same block will have incorrect motionvectors. For example, the nine filled circles in the lower right handcorner of block 750 have correct (top-to-bottom) motion vectors. Theremaining seven empty circles of block 750 have incorrect(top-to-bottom) motion vectors. The correct motion vector for theremaining seven empty circles of block 750 is a left-to-right motionvector. Therefore, when block based motion compensation is performed onblock 750 the motion estimation for the pixels that correspond to theempty circles will be incorrect. The same problem exists in block 760and in block 780.

The improved method of the present invention remedies this problem byindividually considering each pixel and determining whether the motionvector for the block is accurate for the pixel under consideration. Forexample, assume one wishes to interpolate a generated field C betweenprevious frame A and next field B. The pixels for generated field C areusually generated by averaging the motion compensated pixels of frame A(denoted by AMC) and the motion compensated pixels of next field B(denoted by BMC). If the motion vector for an individual pixel iscorrect, then the value of AMC for that pixel and the value of BMC forthat pixel will be very nearly equal. In some cases the two values willbe equal. If, however, the motion vector for an individual pixel is notcorrect, then the value of AMC for that pixel and the value of BMC forthat pixel will not be very nearly equal. The value of AMC and the valueof BMC will be very different.

Comparing the values of AMC and BMC for an individual pixel provides asimple, reliable way to determine whether a particular motion vector iscorrect or incorrect for the individual pixel under consideration. Adetermination that the values of AMC and BMC for an individual pixel arevery different (i.e., not close in value) indicates that the motionvector associated with the pixel is incorrect.

While performing motion compensation on an individual pixel, theimproved method of the present invention saves the values of a number ofadditional adjacent pixels. In one advantageous embodiment of thepresent invention shown in FIG. 8, the additional adjacent pixels whosevalues are saved are located in a three pixel by three pixel array 800.Pixel 1 in array 800 (labeled with a triangle) represents the pixel forwhich motion compensation is being performed. Pixel 2, pixel 3, pixel 4,pixel 5, pixel 6, pixel 7, pixel 8, and pixel 9 in array 800 (labeledwith crosses) represent the additional adjacent pixels whose values aresaved when motion compensation is performed for pixel 1.

The size of the three pixel by three pixel array 800 is by way ofillustration only and should not be construed in any way to limit thescope of the invention. It is clear that the improved method of thepresent invention may be used in connection with arrays havingdimensions other than three pixels by three pixels. The principle ofoperation of the present invention is not limited to a particular sizefor array 800. In general, array 800 may be a n by m array, where n isthe number of rows of pixels and m is the number of columns of pixels.

To understand the operation of the improved method of the presentinvention, consider the placement and use of array 800. FIG. 9illustrates the placement of array 800 on the group of pixels shown inFIG. 7. In particular, FIG. 9 illustrates the placement of array 800 ona portion of block 740 and block 750. It is seen that all of the pixelsin block 740 are represented by empty circles. It is also seen that themotion vector for block 740 (left-to-right) is correct for all of thepixels in block 740. In block 750, however, the motion vector(top-to-bottom) is incorrect for all of the pixels in block 750 that arerepresented is by empty circles.

When motion compensation is performed on pixel 1 of array 800, the valueof AMC (the corresponding motion compensated pixel from previous frameA) and the value of BMC (the corresponding motion compensated pixel fromnext field B) are compared. If the difference between the two values(i.e., the value of AMC minus the value of BMC) is less than apredetermined threshold, then the interpolated pixel value (for thecorresponding pixel 1 in generated field C) will be equal to the averageof the values of AMC and BMC. The method adds the values of AMC and BMCand divides the sum of the values by two to obtain a value for theinterpolated pixel in generated field C.

An appropriate threshold value may be chosen using the fact that a pixeldifference of ten or less between adjacent pixels is not too noticeablea difference. The threshold value may be chosen so that the differencebetween the two values AMC and BMC is less than or equal to ten. Thisthreshold value will insure that the value of the interpolated pixelwill have the appropriate video image quality.

If the difference between the two values (i.e., the value of AMC minusthe value of BMC) is greater than the predetermined threshold, then theinterpolated pixel value (for the corresponding pixel 1 in generatedfield C) will be determined by an alternate method.

When motion compensation is performed on pixel 1 of array 800, the eightvalues of AMC (motion compensated pixels from previous frame A) forpixels 2 through 9 of array 800 are recorded in a memory unit (notshown) in HD upconversion unit 180. Also recorded are the eight valuesof BMC (motion compensated pixels from next field B) for pixels 2through 9 of array 800. In the case illustrated in FIG. 9, pixel 6 andpixel 9 of array 800 correspond to pixels that are represented by filledcircles.

For each of the eight additional pixels (i.e., pixel 2 through pixel 9),the value of AMC (the corresponding motion compensated pixel fromprevious frame A) and the value of BMC (the corresponding motioncompensated pixel from next field B) are compared. If the differencebetween the two values (i.e., the value of AMC minus the value of BMC)is less than a predetermined threshold, then the interpolated pixelvalue (for the corresponding pixel in generated field C) will be equalto the average of the values of AMC and BMC. The method adds the valuesof AMC and BMC and divides the sum of the values by two to obtain avalue for the interpolated pixel in generated field C. For the reasonsdescribed above, the threshold value may be chosen so that thedifference between the two values AMC and BMC is less than or equal toten.

If the difference between the two values (i.e., the value of AMC minusthe value of BMC) is greater than the predetermined threshold for aparticular pixel, nothing is recorded in memory for that pixel location.

After the process described above has been completed for the pixel atthe location of pixel 1 as shown in FIG. 9, the process is repeated (andpixel information is recorded) for each of the other pixels in block740. This is accomplished by sequentially locating pixel 1 of array 800on each of the other pixels in block 740 and performing the methoddescribed above.

The motion compensation process is then applied to the pixels in block750. A comparison of the values of AMC and BMC for the pixelsrepresented by empty circles in block 750 shows that they have anincorrect motion vector. This is indicated by a large difference betweenthe values of AMC and BMC. That is, the values of AMC and BMC are notvery nearly equal.

For the pixels that have incorrect values (due to an incorrect motionvector), a correct value may be obtained for the interpolated pixel fromthe previously recorded value stored in memory. For example, pixel 2,pixel 3, pixel 5, and pixel 8 in block 750 (and three other empty circlepixels outside of array 800 in block 750) have incorrect values becausethe motion vector of block 750 is a top-to-bottom motion vector.However, the recorded values for pixel 2, pixel 3, pixel 5, and pixel 8that were obtained earlier (as previously described) may be used inplace of the incorrect values to obtain correct interpolated values forthe corresponding pixels of generated field C.

If there is no pixel value recorded for a particular pixel location,then some other type of motion compensation method must be used.

The fact that a whole object moves in one direction is useful. If thedirection of movement for part of an object is known, then the directionof movement of other parts of the same object are known as well. Knowingthe correct direction for part of an object enables one to accuratelyinterpolate missing pixels.

The pixel values provided by the improved method of the presentinvention eliminate much of the blurring of the video image that resultsfrom the prior art averaging method. The pixel values provided by theimproved method of the present invention give a sharply defined motioncompensated video image. In cases where the pixel to be selected islocated in an area of an object that is being covered (or that is beinguncovered) during video image motion, the pixel values provided by theimproved method of the present invention help select the better pixel ofthe two pixels choices. This improves the video image quality of covered(and uncovered) regions of the object.

HD upconversion unit 180 performs the improved method of the presentinvention to select the appropriate pixels to make up generated field C.Generated field C is then interpolated (at time T+½) between previousframe A (at time T) and next field B (at time T+1). The interpolationprocess is repeatedly applied to create appropriate output interlacefields ABe, BCe, CDe, DEe and EFe shown in FIG. 3. The output of HDupconversion unit 180 is sent to HD output 190.

FIG. 10 is a flow diagram illustrating a first portion of the improvedmethod of the present invention. The steps of the first portion of theimproved method are collectively referred to with reference number 1000.In the first step the first pixel in n by m array 800 is motioncompensated. The first pixel in array 800 is the pixel for which thevalue of n is one and the value of m is one. In the previously describedexample, the maximum value of n is three and the maximum value of m isthree. It is clear, however, that the values n and m may be selected tohave any positive integer value.

The difference of AMC and BMC for the first pixel is calculated bysubtracting the value of BMC from the value of AMC (step 1010). Then adetermination is made whether the difference is less than the thresholdvalue (decision step 1020). If the difference is less than the thresholdvalue, then the value of the first pixel in generated field C is setequal to the average value of AMC and BMC (step 1030). After step 1030has been completed, control passes to step 1070.

If the difference is not less than the threshold value, then adetermination is made whether there is a recorded value in memory forthe first pixel (decision step 1040). If there is a recorded value inmemory, then the value of the first pixel in generated field C is setequal to the recorded value (step 1050). After step 1050 has beencompleted, control passes to step 1070. If there is no recorded value inmemory, then the value of the first pixel in generated field C isdetermined using an alternate method (step 1060). After step 1060 hasbeen completed, control passes to step 1070.

After step 1030 (or step 1050 or step 1060) has been completed, controlpasses to step 1070 where the difference of AMC and BMC for the nextpixel in array 800 is calculated. The next pixel value of BMC issubtracted from the next pixel value of AMC (step 1070). Then adetermination is made whether the difference for the next pixel is lessthan the threshold value (decision step 1080). If the difference is lessthan the threshold value, then the value of the corresponding pixel ingenerated field C is set equal to the average value of next pixel AMCand next pixel BMC and recorded in memory (step 1090). After step 1090has been completed, control passes to decision step 1095.

If the difference is not less than the threshold value, no value isrecorded for the corresponding pixel in generated field C and controlpasses to decision step 1095. Decision step 1095 determines whether thelast pixel in array 800 has been processed. If the last pixel has notbeen processed, control returns to step 1070 and the next pixel in array800 is processed. If the last pixel in array 800 has been processed, thefirst portion of the improved method of the present invention terminatesits operation (end step).

The first portion of the improved method of the present inventionperforms motion compensation on the first pixel in array 800 and savesthe correct values of the additional pixels that are located withinarray 800. The first portion of the improved method of the presentinvention is repeatedly performed as each pixel in a block of pixels(e.g., block 740) is motion compensated. The information concerningpixel values acquired by the first portion of the improved method isused in the second portion of the improved method, which will now bedescribed.

FIG. 11 is a flow diagram illustrating a second portion of the improvedmethod of the present invention. The steps of the second portion of theimproved method are collectively referred to with reference number 1100.The second portion of the improved method uses the pixel values recordedby the first portion of the improved method to provide improved accuracyduring the process of block based motion compensation.

In the first step the first pixel in a block of pixels (e.g., block 750)is obtained (step 1110). The difference of AMC and BMC for the pixel iscalculated by subtracting the value of BMC from the value of AMC (step1120). Then a determination is made whether the difference is less thanthe threshold value (decision step 1130). If the difference is less thanthe threshold value, then the value of the first pixel in generatedfield C is set equal to the average value of AMC and BMC (step 1140).After step 1140 has been completed, control passes to decision step1180.

If the difference in step 1130 is not less than the threshold value,then a determination is made whether there is a recorded value for thepixel in memory (decision step 1150). If there is not a recorded valuefor the pixel in memory, control passes to step 1170 and the value ofthe pixel is set using an alternate method. After step 1170 has beencompleted, control passes to decision step 1180.

If there is recorded value for the pixel in memory, then the value ofthe pixel is set equal to the recorded value (step 1160). After step1160 has been completed, control passes to decision step 1180.

Decision step 1180 determines whether the last pixel in the block hasbeen processed. If the last pixel has not been processed, the next pixelin the block is obtained (step 1190) and control passes to step 1120where the next pixel is processed. If the last pixel in the block hasbeen processed, the second portion of the improved method of the presentinvention terminates its operation (end step). The second portion of theimproved method of the present invention may be used repeatedly on eachsubsequent block of pixels as required.

The improved method of the present invention has been described using anillustrative example in which there were two different motion vectorspresent. It is clear, however, that the principle of the improved methodof the present invention is not limited to the case of two motionvectors, but is generally applicable to any number of motion vectors(e.g., two, three, four, or more).

Similarly, although the present invention has been described in detailwith respect to the illustrative example of a high definition (HD)progressive to interlace converter, the principle of the improved methodof the present invention is not limited to use with that particular typeof equipment. It is clear that those skilled in the art shouldunderstand that they can make various changes, substitutions andalterations herein without departing from the spirit and scope of theinvention in its broadest form.

What is claimed is:
 1. For use in a video image upconversion unit of thetype that uses motion compensation to generate an interpolated fieldusing motion vectors, a method of motion compensation comprising thesteps of: calculating for a pixel within an array of n pixels by mpixels the difference in value between the value of a correspondingmotion compensated pixel from a previous frame and the value of acorresponding motion compensated pixel from a next field; comparing saiddifference with a threshold value; setting the value of said pixelwithin said array of n pixels by m pixels equal to the average of thevalue of said corresponding motion compensated pixel from said previousframe and the value of said corresponding motion compensated pixel ofsaid next field if the value of said difference is less than saidthreshold value; and recording said value for said pixel within saidarray of n pixels by m pixels.
 2. The method as claimed in claim 1further comprising the steps of: calculating for each of a plurality ofpixels within an array of n pixels by m pixels the difference in valuebetween the value of a corresponding motion compensated pixel from aprevious frame and the value of a corresponding motion compensated pixelfrom a next field; comparing said difference with a threshold value;setting the value of each of said plurality of pixels within said arrayof n pixels by m pixels equal to the average of the value of saidcorresponding motion compensated pixel from said previous frame and thevalue of said corresponding motion compensated pixel of said next fieldif the value of said difference is less than said threshold value; andrecording said values for said plurality of pixels within said array ofn pixels by m pixels.
 3. The method as claimed in claim 2 wherein saidthreshold value is not greater than ten.
 4. The method as claimed inclaim 2 further comprising the steps of: calculating for a pixel withina block of pixels the difference in value between the value of acorresponding motion compensated pixel from a previous frame and thevalue of a corresponding motion compensated pixel from a next field;comparing said difference with a threshold value; setting the value ofsaid pixel within said block of pixels to the average of the value ofsaid corresponding motion compensated pixel from said previous frame andthe value of said corresponding motion compensated pixel of said nextfield, if the value of said difference is less than said thresholdvalue; and setting the value of said pixel within said block of pixelsequal to a value that was previously recorded for said pixel when saidpixel was evaluated as a pixel element within said array of n pixels bym pixels, if the value of said difference is not less than saidthreshold value, and if a recorded value for said pixel was previouslyrecorded.
 5. The method as claimed in claim 4 further comprising thesteps of: calculating for each of a plurality of pixels within saidblock of pixels the difference in value between the value of acorresponding motion compensated pixel from a previous frame and thevalue of a corresponding motion compensated pixel from a next field;comparing said difference with a threshold value; setting the value ofeach of said plurality of pixels within said block of pixels to theaverage of the value of said corresponding motion compensated pixel fromsaid previous frame and the value of said corresponding motioncompensated pixel of said next field, if the value of said difference isless than said threshold value; and setting the value of each of saidplurality of pixels within said block of pixels equal to a value thatwas previously recorded for each of said plurality of pixels when eachof said plurality of pixels was evaluated as a pixel element within saidarray of n pixels by m pixels, if the value of said difference is notless than said threshold value, and if a recorded value for said pixelwas previously recorded.
 6. The method as claimed in claim 5 whereinsaid threshold value is not greater than ten.
 7. For use in a videoimage upconversion unit of the type that uses motion compensation togenerate an interpolated field using motion vectors, a method of motioncompensation comprising the steps of: performing motion compensation ona pixel; determining whether a motion vector assigned to said pixel isincorrect; obtaining a previously recorded pixel value for said pixelwhen it is determined that said motion vector assigned to said pixel isincorrect, said previously recorded pixel value being determined by amethod comprising the steps of: calculating for said pixel when saidpixel is a pixel element within an array of n pixels by m pixels thedifference in value between the value of a corresponding motioncompensated pixel from a previous frame and the value of a correspondingmotion compensated pixel from a next field, comparing said differencewith a threshold value, and setting the value of said pixel within saidarray of n pixels by m pixels equal to the average of the value of saidcorresponding motion compensated pixel from said previous frame and thevalue of said corresponding motion compensated pixel of said next fieldif the value of said difference is less than said threshold value; andsetting the value of said pixel equal to said previously recorded pixelvalue for said pixel.
 8. The method as claimed in claim 7 wherein saidthreshold value is not greater than ten.
 9. The method as claimed inclaim 7 wherein said step of determining whether a motion vectorassigned to said pixel is incorrect comprises the steps of: obtaining avalue of a corresponding motion compensated pixel from a previous frame;obtaining a value of a corresponding motion compensated pixel from anext field; calculating the difference in value between said value ofsaid corresponding motion compensated pixel from said previous frame andsaid value of said corresponding motion compensated pixel from said nextfield; comparing said difference with a threshold value; determiningthat said motion vector assigned to said pixel is incorrect if saiddifference is greater than said threshold value.
 10. The method asclaimed in claim 9 wherein said threshold value is not greater than ten.11. For use in a video image upconversion unit of the type that usesmotion compensation to generate an interpolated field using motionvectors, a method of motion compensation comprising the steps of:performing motion compensation on a first pixel in a plurality of pixelswithin an array of n pixels by m pixels; determining pixel values foreach of said plurality of pixels within said array of n pixels by mpixels other than said first pixel, said pixel values being determinedby a method comprising the steps of: calculating for each of saidplurality of pixels within said array of n pixels by m pixels other thansaid first pixel the difference in value between the value of acorresponding motion compensated pixel from a previous frame and thevalue of a corresponding motion compensated pixel from a next field,comparing said difference with a threshold value, and setting the valueof each of said plurality of pixels within said array of n pixels by mpixels other than said first pixel equal to the average of the value ofsaid corresponding motion compensated pixel from said previous frame andthe value of said corresponding motion compensated pixel of said nextfield if the value of said difference is less than said threshold value;and recording said pixel values for each of said plurality of pixelswithin said array of n pixels by m pixels other than said first pixel.12. The method as claimed in claim 11 Wherein said threshold value isnot greater than ten.
 13. The method as claimed in claim 11 furthercomprising the steps of: performing motion compensation on each of aplurality of pixels in a block of pixels; and determining whether amotion vector assigned to a pixel of said plurality of pixels in saidblock of pixels is incorrect.
 14. The method as claimed in claim 13further comprising the steps of: obtaining a previously recorded pixelvalue for said pixel when it is determined that said motion vectorassigned to said pixel is incorrect; and setting the value of said pixelequal to said previously recorded pixel value for said pixel, where saidpreviously recorded pixel value is one of said pixel values recorded foreach of said plurality of pixels within said array of n pixels by mpixels other than said first pixel.
 15. The method as claimed in claim13 wherein said motion vector assigned to a pixel of said plurality ofpixels in said block of pixels is one of a plurality of motion vectorsassigned to pixels in said block of pixels.
 16. The method as claimed inclaim 13 wherein said array of n pixels by m pixels is repeatedlylocated in different positions with respect to said plurality of pixelsin said block of pixels to obtain pixel values for each of saidplurality of pixels in said block of pixels.
 17. The method as claimedin claim 13 wherein the step of determining whether a motion vectorassigned to a pixel of said plurality of pixels in said block of pixelsis incorrect comprises the steps of: obtaining a value of acorresponding motion compensated pixel from a previous frame; obtaininga value of a corresponding motion compensated pixel from a next field;calculating the difference in value between said value of saidcorresponding motion compensated pixel from said previous frame and saidvalue of said corresponding motion compensated pixel from said nextfield; comparing said difference with a threshold value; determiningthat said motion vector assigned to said pixel of said plurality ofpixels in said block of pixels is incorrect if said difference isgreater than said threshold value.
 18. A high definition progressive tointerlace converter comprising a high definition video imageupconversion unit that uses motion compensation to generate aninterpolated field using motion vectors, wherein said high definitionvideo image upconversion unit is capable of: calculating for a pixelwithin an array of n pixels by m pixels the difference in value betweenthe value of a corresponding motion compensated pixel from a previousframe and the value of a corresponding motion compensated pixel from anext field; comparing said difference with a threshold value; settingthe value of said pixel within said array of n pixels by m pixels equalto the average of the value of said corresponding motion compensatedpixel from said previous frame and the value of said correspondingmotion compensated pixel of said next field if the value of saiddifference is less than said threshold value; and recording said valuefor said pixel within said array of n pixels by m pixels.
 19. The highdefinition progressive to interlace converter as claimed in claim 18wherein said high definition video image upconversion unit is capableof: calculating for each of a plurality of pixels within an array of npixels by m pixels the difference in value between the value of acorresponding motion compensated pixel from a previous frame and thevalue of a corresponding motion compensated pixel from a next field;comparing said difference with a threshold value; setting the value ofeach of said plurality of pixels within said array of n pixels by mpixels equal to the average of the value of said corresponding motioncompensated pixel from said previous frame and the value of saidcorresponding motion compensated pixel of said next field if the valueof said difference is less than said threshold value; and recording saidvalues for said plurality of pixels within said array of n pixels by mpixels.
 20. The high definition progressive to interlace converter asclaimed in claim 19 wherein said high definition video imageupconversion unit is capable of: calculating for a pixel within a blockof pixels the difference in value between the value of a correspondingmotion compensated pixel from a previous frame and the value of acorresponding motion compensated pixel from a next field; comparing saiddifference with a threshold value; setting the value of said pixelwithin said block of pixels to the average of the value of saidcorresponding motion compensated pixel from said previous frame and thevalue of said corresponding motion compensated pixel of said next field,if the value of said difference is less than said threshold value; andsetting the value of said pixel within said block of pixels equal to avalue that was previously recorded for said pixel when said pixel wasevaluated as a pixel element within said array of n pixels by m pixels,if the value of said difference is not less than said threshold value,and if a recorded value for said pixel was previously recorded.
 21. Thehigh definition progressive to interlace converter as claimed in claim20 wherein said high definition video image upconversion unit is capableof: calculating for each of a plurality of pixels within said block ofpixels the difference in value between the value of a correspondingmotion compensated pixel from a previous frame and the value of acorresponding motion compensated pixel from a next field; comparing saiddifference with a threshold value; setting the value of each of saidplurality of pixels within said block of pixels to the average of thevalue of said corresponding motion compensated pixel from said previousframe and the value of said corresponding motion compensated pixel ofsaid next field, if the value of said difference is less than saidthreshold value; and setting the value of each of said plurality ofpixels within said block of pixels equal to a value that was previouslyrecorded for each of said plurality of pixels when each of saidplurality of pixels was evaluated as a pixel element within said arrayof n pixels by m pixels, if the value of said difference is not lessthan said threshold value, and if a recorded value for said pixel waspreviously recorded.
 22. The high definition progressive to interlaceconverter as claimed in claim 21 wherein said threshold value is notgreater than ten.
 23. The high definition progressive to interlaceconverter as claimed in claim 18 wherein said high definition videoimage upconversion unit is capable of: performing motion compensation ona first pixel in a plurality of pixels within an array of n pixels by mpixels; determining pixel values for each of said plurality of pixelswithin said array of n pixels by m pixels other than said first pixel;recording said pixel values for each of said plurality of pixels withinsaid array of n pixels by m pixels other than said first pixel;performing motion compensation of each of a plurality of pixels in ablock of pixels; determining whether a motion vector assigned to a pixelof said plurality of pixels in said block of pixels in incorrect;obtaining a previously recorded pixel value for said pixel when it isdetermined that said motion vector assigned to said pixel is incorrect;and setting the value of said pixel equal to said previously recordedpixel value for said pixel, where said previously recorded pixel valueis one of said pixel values recorded for each of said plurality ofpixels within said array of n pixels by m pixels other than said firstpixel.
 24. A high definition receiver comprising a high definitionprogressive to interlace converter comprising a high definition videoimage upconversion unit that uses motion compensation to generate aninterpolated field using motion vectors, wherein said high definitionvideo image upconversion unit is capable of: calculating for a pixelwithin an array of n pixels by m pixels the difference in value betweenthe value of a corresponding motion compensated pixel from a previousframe and the value of a corresponding motion compensated pixel from anext field; comparing said difference with a threshold value; settingthe value of said pixel within said array of n pixels by m pixels equalto the average of the value of said corresponding motion compensatedpixel from said previous frame and the value of said correspondingmotion compensated pixel of said next field if the value of saiddifference is less than said threshold value; and recording said valuefor said pixel within said array of n pixels by m pixels.
 25. The highdefinition receiver as claimed in claim 24 wherein said high definitionvideo image upconversion unit is capable of: calculating for each of aplurality of pixels within an array of n pixels by m pixels thedifference in value between the value of a corresponding motioncompensated pixel from a previous frame and the value of a correspondingmotion compensated pixel from a next field; comparing said differencewith a threshold value; setting the value of each of said plurality ofpixels within said array of n pixels by m pixels equal to the average ofthe value of said corresponding motion compensated pixel from saidprevious frame and the value of said corresponding motion compensatedpixel of said next field if the value of said difference is less thansaid threshold value; and recording said values for said plurality ofpixels within said array of n pixels by m pixels.
 26. The highdefinition receiver as claimed in claim 25 wherein said high definitionvideo image upconversion unit is capable of: calculating for a pixelwithin a block of pixels the difference in value between the value of acorresponding motion compensated pixel from a previous frame and thevalue of a corresponding motion compensated pixel from a next field;comparing said difference with a threshold value; setting the value ofsaid pixel within said block of pixels to the average of the value ofsaid corresponding motion compensated pixel from said previous frame andthe value of said corresponding motion compensated pixel of said nextfield, if the value of said difference is less than said thresholdvalue; and setting the value of said pixel within said block of pixelsequal to a value that was previously recorded for said pixel when saidpixel was evaluated as a pixel element within said array of n pixels bym pixels, if the value of said difference is not less than saidthreshold value, and if a recorded value for said pixel was previouslyrecorded.
 27. The high definition receiver as claimed in claim 26wherein said high definition video image upconversion unit is capableof: calculating for each of a plurality of pixels within said block ofpixels the difference in value between the value of a correspondingmotion compensated pixel from a previous frame and the value of acorresponding motion compensated pixel from a next field; comparing saiddifference with a threshold value; setting the value of each of saidplurality of pixels within said block of pixels to the average of thevalue of said corresponding motion compensated pixel from said previousframe and the value of said corresponding motion compensated pixel ofsaid next field, if the value of said difference is less than saidthreshold value; and setting the value of each of said plurality ofpixels within said block of pixels equal to a value that was previouslyrecorded for each of said plurality of pixels when each of saidplurality of pixels was evaluated as a pixel element within said arrayof n pixels by m pixels, if the value of said difference is not lessthan said threshold value, and if a recorded value for said pixel waspreviously recorded.
 28. The high definition receiver as claimed inclaim 27 wherein said threshold value is not greater than ten.
 29. Thehigh definition progressive to interlace converter as claimed in claim24 wherein said high definition video image upconversion unit is capableof: performing motion compensation on a first pixel in a plurality ofpixels within an array of n pixels by m pixels; determining pixel valuesfor each of said plurality of pixels within said array of n pixels by mpixels other than said first pixel; recording said pixel values for eachof said plurality of pixels within said array of n pixels by m pixelsother than said first pixel; performing motion compensation of each of aplurality of pixels in a block of pixels; determining whether a motionvector assigned to a pixel of said plurality of pixels in said block ofpixels in incorrect; obtaining a previously recorded pixel value forsaid pixel when it is determined that said motion vector assigned tosaid pixel is incorrect; and setting the value of said pixel equal tosaid previously recorded pixel value for said pixel, where saidpreviously recorded pixel value is one of said pixel values recorded foreach of said plurality of pixels within said array of n pixels by mpixels other than said first pixel.
 30. A signal comprising: an outputsignal of a high definition progressive to interlace convertercomprising a high definition video image upconversion unit that usesmotion compensation to generate an interpolated field using motionvectors, wherein said high definition video image upconversion unitgenerates said output signal by: calculating for a pixel within an arrayof n pixels by m pixels the difference in value between the value of acorresponding motion compensated pixel from a previous frame and thevalue of a corresponding motion compensated pixel from a next field;comparing said difference with a threshold value; setting the value ofsaid pixel within said array of n pixels by m pixels equal to theaverage of the value of said corresponding motion compensated pixel fromsaid previous frame and the value of said corresponding motioncompensated pixel of said next field if the value of said difference isless than said threshold value; and recording said value for said pixelwithin said array of n pixels by m pixels.
 31. The signal as claimed inclaim 30 wherein said high definition video image upconversion unitgenerates said output signal by: calculating for each of a plurality ofpixels within an array of n pixels by m pixels the difference in valuebetween the value of a corresponding motion compensated pixel from aprevious frame and the value of a corresponding motion compensated pixelfrom a next field; comparing said difference with a threshold value;setting the value of each of said plurality of pixels within said arrayof n pixels by m pixels equal to the average of the value of saidcorresponding motion compensated pixel from said previous frame and thevalue of said corresponding motion compensated pixel of said next fieldif the value of said difference is less than said threshold value; andrecording said values for said plurality of pixels within said array ofn pixels by m pixels.
 32. The signal as claimed in claim 31 wherein saidhigh definition video image upconversion unit generates said outputsignal by: calculating for a pixel within a block of pixels thedifference in value between the value of a corresponding motioncompensated pixel from a previous frame and the value of a correspondingmotion compensated pixel from a next field; comparing said differencewith a threshold value; setting the value of said pixel within saidblock of pixels to the average of the value of said corresponding motioncompensated pixel from said previous frame and the value of saidcorresponding motion compensated pixel of said next field, if the valueof said difference is less than said threshold value; and setting thevalue of said pixel within said block of pixels equal to a value thatwas previously recorded for said pixel when said pixel was evaluated asa pixel element within said array of n pixels by m pixels, if the valueof said difference is not less than said threshold value, and if arecorded value for said pixel was previously recorded.
 33. The signal asclaimed in claim 32 wherein said high definition video imageupconversion unit generates said output signal by: calculating for eachof a plurality of pixels within said block of pixels the difference invalue between the value of a corresponding motion compensated pixel froma previous frame and the value of a corresponding motion compensatedpixel from a next field; comparing said difference with a thresholdvalue; setting the value of each of said plurality of pixels within saidblock of pixels to the average of the value of said corresponding motioncompensated pixel from said previous frame and the value of saidcorresponding motion compensated pixel of said next field, if the valueof said difference is less than said threshold value; and setting thevalue of each of said plurality of pixels within said block of pixelsequal to a value that was previously recorded for each of said pluralityof pixels when each of said plurality of pixels was evaluated as a pixelelement within said array of n pixels by m pixels, if the value of saiddifference is not less than said threshold value, and if a recordedvalue for said pixel was previously recorded.
 34. The signal as claimedin claim 33 wherein said threshold value is not greater than ten. 35.The signal as claimed in claim 30 wherein said high definition videoimage upconversion unit generates said output signal by: performingmotion compensation on a first pixel in a plurality of pixels within anarray of n pixels by m pixels; determining pixel values for each of saidplurality of pixels within said array of n pixels by m pixels other thansaid first pixel; recording said pixel values for each of said pluralityof pixels within said array of n pixels by m pixels other than saidfirst pixel; performing motion compensation of each of a plurality ofpixels in a block of pixels; determining whether a motion vectorassigned to a pixel of said plurality of pixels in said block of pixelsin incorrect; obtaining a previously recorded pixel value for said pixelwhen it is determined that said motion vector assigned to said pixel isincorrect; and setting the value of said pixel equal to said previouslyrecorded pixel value for said pixel, where said previously recordedpixel value is one of said pixel values recorded for each of saidplurality of pixels within said array of n pixels by m pixels other thansaid first pixel.